Define Response Spectrum Functions

Form: Define Response Spectrum Functions

Use the Define menu > Functions > Response Spectrum Functions command to display the Define Response Spectrum Functions form and add, modify, or delete a response-spectrum function.

A response-spectrum function is simply a list of period versus spectral-acceleration values. In SAP2000, the acceleration values in the function are assumed to be normalized; that is, the functions themselves are not assumed to have units. Instead, the units are associated with a scale factor that multiplies the function and that is specified when the response-spectrum load case is defined.

Note: By default, the program pre-defines a unit constant response-spectrum function. This function may be modified or deleted.

Important: A response-spectrum function can be defined for any period range, T0 to Tn. For all periods less than the first given period T0, the function value is assumed to be constant at the function value specified for T0. For all periods greater than the last given period Tn, the function value is assumed to be constant at the function value specified for Tn.

1. Click the Define menu > Functions > Response Spectrum Functions command to access the Define Response Spectrum Function form.

2. Use the following buttons to complete the appropriate action:

   • Add New Function button

   • 1. Use the Choose the Function Type to Add drop-down list to select the type of function to be added. For more information, see:

        • Spectrum from File

        • User Spectrum

        • Code-Specific Response-Spectrum Functions

     2. Click the Add Function button. This opens the appropriate form to enter the data needed to define the function. Use the above hyperlinks to access information about the specific forms, or display the form and click the F1 key to access the Help topic specific to the form being displayed.

   • Modify/Show Spectrum button

   • 1. Highlight the name of the function to be modified in the Response Spectra display list.

     2. Click the Modify/Show button to access the same form as was used to define the function.

     3. Use the form to make the necessary changes. The function type cannot be changed, except a function can be changed to a user-defined function type. Topics describing the various function forms are accessible using the hyperlinks in the Add New Function button description above or by displaying the form and using the F1 key.

   • Delete Spectrum button

   • 1. Highlight the name of the function to be deleted in the Response Spectra display list.

     2. Click the Delete Spectrum button.

Example:  Use of this command is demonstrated in Problem Y and Problem Z.